PLASMA TRANSPORT OF LIPIDS AND LIPOPROTEIN PROTEINS IN DOGS TREATED WITH TRITON WR-1339
Angelo Scanu, Irvine H. Page
J Clin Invest. 1962;41(3):495-504. https://doi.org/10.1172/JCI104503.
Research Article
Find the latest version: https://jci.me/104503/pdf Journal of Clinical Investigation Vol. 41, No. 3, 1962 PLASMA TRANSPORT OF LIPIDS AND LIPOPROTEIN PROTEINS IN DOGS TREATED WITH TRITON WR-1339* By ANGELO SCANU f AND IRVINE H. PAGE (From the Research Division of the Cleveland Clinic Foundation, Cleveland, Ohio) (Submitted for publication July 27, 1961; accepted October 27, 1961)
Production of hyperlipemia after administration On the basis of the above observations and in an of Triton' WR-1339, a non-ionic surface-active attempt to better define the type of lipoprotein ab- agent, has been described in rabbits (1), guinea normality in the plasma of dogs given Triton, ca- pigs (1, 2), mice (3), and rats (4). A similar nine serum lipoproteins, separated by ultracentri- observation has been recently extended to dogs fugation, were isotopically labeled in each of their (5). These latter animals, after prolonged ad- components, and their plasma transport and distri- ministration of the detergent in a dose of 250 mg bution among the various ultracentrifugal lipopro- per kg every fourth day, died within a period of tein classes was studied in dogs treated with 2 to 3 months (5). Pathological studies showed: Triton WR-1339. The results of these studies a) large accumulation of lipids in the subintima are presented herein. of aorta and coronary arteries; b) marked lipid engulfment of the reticuloendothelial cells of liver, MATERIALS AND METHODS spleen, and lymph nodes; and c) diffuse depletion Male mongrel dogs weighing from 9 to 14 kg were of fat stores. According to the plasma lipid levels, used. They were fed a commercial diet (5). Hyper- the course of the disease could be divided into a lipemia was produced by intravenous administration of normolipemic stage of 2 to 3 weeks' duration, fol- Triton (250 mg per kg every fourth day) according to the method of Scanu and co-workers (5). Another lowed by a hyperlipemic stage of 4 to 8 weeks' du- group of dogs was kept as a control. ration, characterized by a progressive rise of all Ultracentrifugal methods of separation and purifica- plasma lipids until death of the animals. tion of serum lipoproteins were the same as previously In vitro studies from this laboratory (6) have described (7). We will refer to lipoproteins of density furnished evidence that, after addition of Triton (D) < 1.006 as chylomicrons, D 1.006-1.063 as fi-lipo- proteins, and D 1.063-1.21 as al-lipoprotein. to canine serum lipoproteins, the detergent com- Preparation of labeled materials for injection into re- bines preferentially with their lipid moiety, weak- cipient dogs. In vitro labeling with I.81 of the protein ening the association between protein and lipid. moiety of both 8LP 2 and aLP was performed according Similar alterations were produced in chylomicrons, to McFarlane (8). Free iodide was removed by passing where Triton was able to displace part of their the radioiodinated protein three times through an anion exchange resin, Ioresin (Abbott Labs., North Chicago, protein moiety from its association with lipids (6). Ill.). We estimated that the labeled protein had about 1 In dogs treated with Triton the establishment of atom of iodine per molecule. the hyperlipemia was accompanied by profound C1'-labeling of lipoprotein cholesterol was performed changes in the ultracentrifugal lipoprotein pattern according to Avigan (9) by incorporating in vitro cho- with disappearance of the high-density class and lesterol-4-C' into the ultracentrifugally separated ca- nine serum lipoproteins.3 In these experiments 10 lsc of accumulation of lipids in the very low-density labeled cholesterol per mg of lipoprotein protein was lipoproteins (5). used. Pn-labeling4 of the lipoprotein phospholipids was per- * Supported by grants of the U. S. Public Health formed in vivo. Normal fasting dogs were each given Service (H-96) and the Cleveland Area Heart Society. A preliminary report has appeared in abstract form in 2 The abbreviations used in the text are: pLP = fi-lipo- Clin. Res. 1961, 9, 188. protein, aLP = a,-lipoprotein, and aP = the protein of f Present address: University of Chicago Hospitals, aLP after removal of the lipid. The University of Chicago School of Medicine, Chicago, 3 Cholesterol-4-C14 purchased from Volk Radiochemical Ill. Co., Chicago, Ill. 1 Triton WR-1339, Winthrop and Stearns, New York, 4 P" obtained from Abbott Laboratories, North Chicago, N. Y. Ill. 495 496 ANGELO SCANU AND IRVINE H. PAGE intravenously 10 mg of P', and approximately 12 hours selectively retains unbound iodine, the effluent from the later 500 ml of venous blood was withdrawn. The sera column was practically free of radioactivity. were ultracentrifuged at D 1.21 to float all classes of Chemical analyses. Protein was measured according to lipoproteins. These lipoproteins were washed twice in Lowry, Rosebrough, Farr and Randall (13), cholesterol a medium of D 1.21 each time for 24 hours and the final according to Abell, Levy, Brodie and Kendall (14), and product dialyzed against large volumes of 0.15 M NaCl. triglycerides according to Van Handel and Zilversmit To obtain C"4-labeled triglycerides, the technique of (15). Phospholipids were calculated as 25 times the Havel and Fredrickson (10) was followed. Normal value of the lipid phosphorus obtained by the method of dogs, receiving a saline infusion, had their thoracic duct Fiske and Subbarow (16). The method of Dole (17) cannulated (11) and were given 100 Ac of the sodium was used for plasma free fatty acids. In the analysis of soap of palmitic-l-CG' acid 8 mixed in 50 ml of commer- plasmas from both normal and Triton-treated dogs, the cial 30 per cent cream through a stomach tube. Lymph factor of error of this method was around 1 per cent. was collected for 6 hours; chylomicrons were separated Electrophoretic studies. We performed these on both as was done for serum chylomicrons (12). filter paper according to Durrum (18) and starch-gel ac- Experiments were also conducted by using a com- cording to Smithies (19), using the discontinuous system mercial product of radioiodinated triolein, Raolein, I.V.5 of buffers of Poulik (20). Details of the techniques and Before intravenous use the content of each vial (triolein, staining procedures have been previously reported (7). 287 mg; radioactivity, 75 /sc) was mixed with 2 ml of Measurements of radioactivity. Serum samples (1 ml), 1 per cent solution in saline of Lipomul-Oral.6 A fine obtained from dogs injected with I1"-labeled materials, emulsion was thus obtained. were counted in a sodium-crystal scintillation detector For studies of plasma free fatty acids (FFA) an al- (Tracer-Lab) with a counting efficiency of approximately bumin-C1' palmitate complex was used. This was pre- 33 per cent. C"-labeled FFA and triglycerides, after sol- pared by mixing 100 ,uc of palmitic-l-C' acid (1.95 mc vent extraction from plasma, were plated on lens paper- per mmole) after neutralization with 0.1 N NaOH, and covered stainless steel planchets after addition of pal- approximately 1 g of canine serum albumin.7 mitic acid to a final weight of 15 mg per planchet (21). Labeling of Triton with I' was performed as previously Cholesterol-4-C" was plated on aluminum planchets as described (6). digitonide and counted at infinite thickness. Lipid ex- Procedure of in zivo experiments. Approximately 1 tracts containing P'-phospholipids were mixed with 100 month before administration of the labeled material, mg of commercial lecithin and plated on stainless steel plasma volume was determined in each dog, according to planchets. Counting of C1'-cholesterol and P'2-phospho- the isotope dilution principle, 10 minutes after intravenous lipids was performed in a windowless gas-flow GM tube injection of I"1'-labeled canine serum albumin (15 /Lc). (Tracer-Lab) with a background of about 22 cpm. The At the same time the hematocrit value was determined. counting error was ± 3 per cent. After injection of one of the labeled materials, hemato- crit readings were used to assess possible changes in RESULTS plasma volume. No significant changes were observed in either normal or Triton-treated animals. 1. Normolipemia All radioactive materials were inj ected intravenously, usually in doses of 100 utc, and blood samples were taken The duration of the normolipemic stage being at intervals to determine their rate of disappearance from only 2 to 3 weeks (5), long-term studies with la- circulation. The distribution of radioactivity among the beled lipoproteins could not be performed. The various lipoproteins, ultracentrifugally separated, was rates of disappearance of intravenously injected determined. The dogs injected with I"1'-labeled lipo- protein protein or I"-Triton received 10 drops of Lugol's C14-labeled triglycerides, I131-triolein, and albumin- solution in their drinking water daily to prevent radio- bound palmitate-1-C14 were all within the limits iodine uptake by the thyroid. The urinary excretion of of the values reported in the following section for radioactivity was also determiined. The radioactivity was normal dogs. The distribution of radioactivity found related to free iodine; in fact, when urines were among the various lipoprotein classes was normal. filtered through an anion exchange resin (Ioresin), which 6 Raolein, I. V., Abbott Labs., North Chicago, Ill. We 2. Hyperlipemia (4 to 6 weeks' duration) are deeply indebted to Dr. B. Eberle for the generous sup- ply of the radioiodinated material. Each vial contained The rates of disappearance from circulation and 287 mg triolein, 1,657 mg glycerol, and 55 mg lecithin. plasma distribution of various labeled lipids in- A chromatographic analysis of this product has been jected intravenously are summarized in Table I. reported by Lakshminarayana and co-workers (Fed. For each study two normal and two Triton-treated Proc. 1959, 18, 269) and found to contain mainly triglycer- ides and appreciable proportions of mono- and diglycerides. dogs were used. 6tUpjohn Co., Kalamazoo, Mich. Cholestero1-4-C14 (Figure 1) was removed from 7 Pentex Co., Kankakee, Ill. the plasma of normal animals with half-times of LIPID TRANSPORT IN TRITON-TREATED DOGS 497
TABLE I Rates of disappearance from circulation and plasma distribution of various labeled lipids after their intravenous injection into normal and Triton-treated dogs
Distribution of radioactivity Plasma Plasmat Plasma D 1.006- D 1.063- Dog* Wt volume conc. pool t4 D <1.006 1.063 1.21 D.>1.21 kg ml mg/mi mg days % % % % Cholesterol Cholesterol-4-C14 1, N 12 420 1.25 525 8.7 2.4 6.6 91.0 2, N 10 400 1.87 748 7.8 2.0 7.9 90.1 3, T 10 380 13.70 5,206 9.0 23.0 73.0 4.0 A 4, T 11 400 18.20 7,280 10.0 25.4 68.0 6.6 Phospholipids hrs Pn-phospholipids 5, N 11 420 3.0 1,260 34 2.6 4.4 93.0 6, N 12 450 3.2 1,440 38 1.6 5.7 92.7 7, T 11 440 15.4 6,676 54 22.3 70.6 7.1 B 8, T 11 420 17.3 7,266 44 28.3 61.4 10.3 Triglycerides min I'll-triolein 9, N 10 350 0.40 180 9 95.0 5.0 10, N 10 460 0.46 211 11 97.0 3.0 11, T 12 420 3.20 1,344 36 98.0 2.0 C 12, T 11 410 8.60 3,526 80 96.0 4.0 Free fatty acids$ min Na palmitate-1-CI4 13, N 10 420 0.32 134 2.0 6.4 18.4 75.2 14, N 11 435 0.27 117 2.0 8.7 19.1 72.4 15, T 10 435 1.13 492 2.2 70.2 29.8 D 16, T 11 450 1.20 540 2.0 74.3 35.7
* N = normal, T = Triton-treated. t Because of the changes in plasma lipid levels produced by Triton, the lipid values reported in the table are an average of those collected within the experimental period: 16 days for A, 72 hours for B, 60 minutes for C, and 6 minutes for D. I The values are expressed in pEq/ml. 8.7 and 7.8 days. In the Triton-treated animals D 1.063-1.21 lipoprotein; in the Triton-treated the plasma disappearance of the injected labeled dogs about 70 per cent was found in the D 1.006- cholesterol was more difficult to evaluate because 1.063 and about 24 per cent in the D < 1.006 of the significant changes in blood cholesterol class (Table I, A). concentrations during the 16-day experimental PS2-phospholipids were removed from circula- period. By plotting values of specific radioactivity tion (Figure 2) at a lower rate in Triton-treated of plasma cholesterol against time, the curve shown animals (ti, 54 and 44 hours) than in normal ani- in Figure 1 was obtained. From this curve we mals (ti, 34 and 38 hours). In the relatively calculated half-time values of 9 and 10 days, short experimental period no significant changes in considering only the tract of the curve (from ex- plasma phospholipids were observed. The distri- perimental days 4 to 8) in which no significant bution of radioactivity (Table I, B) differed con- changes in blood cholesterol were observed. When siderably from that of normal animals and was a correction factor was applied for the dilution in similar to that observed in the C14-cholesterol ex- the plasma radioactivity produced by the rise in periments. Triton-treated dogs had a plasma pool cholesterol, half-time values increased in the two of phospholipids about seven times higher than dogs 5 and 10 per cent, respectively. that in normal animals (Table I, B). In Triton-treated dogs plasma cholesterol was I131-triolein plasma removal showed a major dif- about 10 times higher than normal and was par- ference between the two groups of animals (Fig- titioned among plasma lipoproteins, separated by ure 3); it was considerably delayed in those given ultracentrifugation, in a manner different from Triton (ti, 36 and 80 minutes) as compared with that in normal animals; in normal dogs most of normal (tj, 9 and 11 minutes). The rate of re- the labeled cholesterol (91 per cent) was in the moval of I1-triolein was affected by each dose of 498 ANGELO SCANU AND IRVINE H. PAGE Triton. During the hours immediately after its 100 100 injection the delay in egress of the labeled fat was five to six times greater than the values obtained 2 or 3 days later. Further, a greater delay of re- moval of I131-triolein was observed with increasing severity of the hyperlipemia which, in turn, was proportional to the number of injections of the 40 40 detergent. In both normal and Triton-treated animals plasma radioactivity was confined mostly to the D < 1.006 lipoprotein class (Table I, C). This finding was of particular significance in the Triton- treated dogs, since most of the triglycerides car- E ried by the D 1.006-1.063 lipoproteins failed to mix with the injected I131-triolein. For comparison similar experiments were con- ducted in both normal and Triton-treated dogs 00 10 with C14-labeled glycerides. A marked delay of a: these labeled lipids was observed in the Tritonized 0._ animals. After the first 20-minute period the 0 a. curve of disappearance became more flat, prob- 0 ably related to the plasma recycling of some of the ' 5 labeled molecules. In separate experiments samples of I131-triolein (287 mg), with a total radioactivity of 75 uc, ' 3 were first mixed in vitro with various amounts of
2
1 24 48 72 TIME IN HOURS FIG. 2. DISAPPEARANCE FROM CIRCULATION OF P2- PHOSPHOLIPIDS IN NORMAL AND TRITON-TREATED DOGS. Arrows indicate time of administration of Triton.
Triton (1 to 100 mg) and then injected intra- venously into normal animals. It was found that samples containing the higher quantities of de- tergent were removed from circulation at lower rates. Albumin-bound palmitate-l-C14 was injected t - I- .,, . intravenously into two normal and two Triton- 2 4 6 8 10 12 14 16 treated dogs, and blood samples were taken after Time in days 0.5 1, 1.5, 2, 3, 4, and 8 minutes. All animals FIG. 1. DISAPPEARANCE FROM CIRCUL.ATION OF CHO- 5, LESTEROL-4-C1' IN NORMAL AND TRITOIq-TREATED DS. exhibited about the same plasma removal rate of Arrows indicate time of administration c)f Triton. approximately 2 minutes (Figure 4). A marked LIPID TRANSPORT IN TRITON-TREATED DOGS 499 difference between the two groups of animals was 200 found in the size of the plasma FFA pool, which was about three times higher in the Triton-treated animals, and in the distribution of radioactivity among the plasma proteins (Table I, D). The 100 100 radioactivity in the plasma of animals receiving Triton was mostly contained in the low-density lipoprotein class floating at D < 1.063, whereas in the normal animals it was found bound principally & 50- 50 to the fraction of serum sedimenting at D 1.21 and w better defined by paper and starch electrophoretic analysis as albumin. 4: Because of the preferential association of the V radiopalmitate with the low-density plasma lipo- C._a:l-. proteins of Triton-treated animals, experiments were performed to compare, after intravenous ad- u0 ministration of albumin-bound C14-palmitate, the 0 rate of disappearance from circulation of radio- : 10 activity bound to albumin and that bound to lipo- FLUI 1 °- 1 0 iv 100 100
5 5 50 3- 3
~0V .0 2- 2 S._
c
:0 - 0 ._0 104 Ift 2 4 6 8 ._ 0 Time in minutes To FIG. 4. DISAPPEARANCE FROM CIRCULATION OF ALBU- MIN-BOUND PALMITATE-1-C1' IN NORMAL AND TRITON- 5 TREATED DOGS.
proteins. The values were essentially similar with an average half-time of 2 minutes. When ,8-lipoprotein and a-lipoprotein labeled in the protein moiety with I131 were injected in- travenously into Triton-treated animals, their rate of removal from plasma had an average half-time of 2.3 and 4.7 days, respectively (Figure 5). 20 40 60 These figures were similar to those obtained in Time in minutes normal dogs (Table II). The size of the plasma FIG. 3. DISAPPEARANCE FROM CIRCULATION OF P"-TRO- pool of the lipoprotein proteins was also similar LEIN IN NORMAL AND TRITON-TREATED DOGS. in the two groups of animals (Table II). 500 ANGELO SCANU AND IRVINE H. PAGE
TABLE II Rates of disappearance from circulation and plasma distribution of lipoproteins labeled in the protein moiety with I131 after their intravenous injection into normal and Triton-treated dogs
Distribution of radioactivity Plasma Plasma Plasma D 1.006- D 1.063- Dog Wt volume conc. pool tj D
* The values refer to the protein moiety of all classes of serum lipoproteins floating at D 1.21.
Marked differences were observed in the distri- bution of plasma radioactivity. After the adminis- tration of either labeled 3LP or aLP proteins, plasma radioactivity was confined in normal dogs to either the JLP or aLP class, respectively. In the Triton-treated dogs, regardless of which lipo- protein protein was injected, the radioactivity was found distributed between the low-density lipo- proteins of D < 1.006 (average, 33 per cent) and 5 T/ = . T/2 3.5 doys D 1.006-1.063 (average, 60 per cent). The same type of radioactivity distribution was observed in 2 4 10 10 the plasma of dogs given aP-IlJ3 (Table II). When ultracentrifugally separated plasma lipo- Ti22.2dayi from were ana- 05 proteins dogs treated with Triton lyzed by starch-gel electrophoresis, lipid and pro- tein moieties moved in the opposite directions.
TABLE III Rates of disappearance from circulation of I13-Triton after intravenous injection into normal and Triton-treated dogs
Distribution of radioactivity
2 4 6 8 10 12? Dog Wt t4 D<1.006 D 1.006-1.063 D 1.063-1.21 D>1.21 Time in days kg days % % % % 1, N 10 4.2 9.0 91.0 FIG. 5. DISAPPEARANCE FROM CIRCULATION OF jSLP- 2, N 11 3.8 6.8 93.2 3, T 11 2.8 35 62 3 I' AND aLP-Im IN NORMAL AND TRITON-TREATED DOGS. 4, T 12 2.7 28 68 4 Arrows indicate time of administration of Triton. LIPID TRANSPORT IN TRITON-TREATED DOGS 501 In the normal dogs the two moieties moved to- is of interest. This finding and the fact that the gether. rate of plasma removal of these proteins from cir- I131-Triton, given intravenously to two normal culation was similar in both normal and Triton- dogs, left the circulation in an average half-time treated animals seem to suggest that their metabo- of 4 days. The radioactivity was mostly in the lism was not affected by the administration of the D 1.063-1.21 lipoprotein class. In two Triton- detergent. This assumption seems corroborated treated dogs (Table III), the radioactivity disap- by recent studies by Radding and Steinberg (27) peared from plasma at a slightly faster rate (aver- showing that rats given Triton have a normal age, 2.75 days) and was distributed between the hepatic synthesis of lipoprotein protein, in con- lipoproteins of D < 1.006 (33 per cent) and trast to the marked increase in the rate of choles- D 1.006-1.063 (67 per cent). terol synthesis. Previous studies from this laboratory have DISCUSSION shown that Triton induces a dissociation of the protein and lipid moieties of plasma lipoproteins Studies in mice and rabbits by Hirsch and Kell- in vitro (6) and produces in vivo a profound ner (3, 22) and in rats by Friedman and Byers change in the spectrum of circulating lipoproteins (4, 23), supported the evidence for the hypothesis with accumulation of the low-density classes un- that Triton hyperlipemia is caused by primary usually rich in lipids (5). In the present studies, physical or chemical changes produced in the when the labeled proteins of either 83LP or aLP plasma lipids by the administration of the deter- were injected into animals receiving Triton, the gent, leading in turn to their accumulation in the radioactivity was found distributed between lipo- blood stream. This concept seems to apply to protein fractions floating at solvent densities of plasma glycerides in view of the experimental find- < 1.006 and 1.006-1.063. In normal animals each ing that Triton-treated rats have a delayed removal of the injected labeled proteins traveled with its of injected I'31-triolein (24) and C14-labeled chylo- own lipoprotein class (Table II). Thus, in Tri- microns (25), results now corroborated by our ton-treated dogs, plasma lipoprotein proteins ap- studies in dogs. According to Friedman and pear to have lost the property of combining specifi- Byers (23) the primary accumulation of plasma cally with their own lipoprotein class to become triglycerides would lead to a rise of the plasma loosely associated with the main bulk of plasma levels of cholesterol and phospholipids by favoring lipids. This interpretation seems validated by the their mobilization from hepatic and extrahepatic observation that in Triton-treated dogs, protein sources and sequestration in the circulating plasma. and lipid moieties of ultracentrifugally prepared Experimental work by Frantz and Hinkelman plasma lipoproteins migrated differently in an elec- (26) has clearly shown that rats given Triton trical field. Further, when labeled Triton was in- have a marked increase of the hepatic cholesterol jected into Triton-treated dogs the radioactivity synthesis, a factor likely to be largely responsible was contained only in the plasma fractions very for the hypercholesterolemia in these animals. rich in lipids. Our findings in dogs treated with Triton and in- In fasting, the major source of FFA is in adi- jected with labeled cholesterol and phospholipids pose tissue (28). The fact that fasting plasma do not seem to indicate that these lipids are locked FFA levels were elevated in Triton-treated dogs in the circulating plasma but tend to support the led us previously to postulate (5) that this in- hypothesis that the hypercholesterolemia and hy- crease was an expression of an enhanced lipid perphospholipidemia of Tritonized dogs are sec- mobilization from fat depots. This hypothesis ondary to an imbalance between their rate of syn- seems corroborated by recent studies of Byers, thesis and their rate of removal from circulation, Cady and Friedman (29) and by our present ex- the former exceeding the latter. periments conducted with albumin-bound palmi- The observation that Triton-treated dogs main- tate-1-C14. If we assume that in both of these ex- tain a normal level of circulating lipoprotein pro- periments a steady state existed during the period teins, in spite of the large rise of all plasma lipids, of rapid disappearance from circulation of the la- 502 ANGELO SCANU AND IRVINE H. PAGE beled palmitate, it could be calculated8 that Triton- - HYPOTHETICAL MECHANISM OF TRITON HYPERLIPEMIA treated animals had a turnover rate of FFA two to Lipoprotein Normol + three times larger than normal animals had. This T G leads us to postulate that animals receiving Triton have an enhanced metabolic in adi- activity the LIVER ADIPOSE TISSUE pose tissue which may explain why dogs chroni- cally treated with Triton ultimately exhibited a diffuse depletion of their fat stores (5). FFA Our present studies have confirmed previous Albumin findings (30) that in Triton-treated dogs there [ -RITON RES are two plasma FFA compartments, one bound Triton to albumin, the other (the major one) bound to lipoproteins. It now appears, from the radioiso- topic data, that plasma FFA removal from each LIVER K of these compartments is very rapid, indicating that association of FFA with albumin is not es- sential for their plasma transport and that lipo- proteins can act as their major carriers Whenever conditions interfere with their combination with albumin. Plasma lipoproteins are the major car- riers of FFA in patients with the nephrotic syn- FFA drome due to lack of circulating plasma albumin FIG. 6. HYPOTHETICAL MECHANISM OF TRITON (31). In the Triton-treated dogs, however, the HYPERLIPEMIA. plasma levels of albumin are normal (5). responds by increasing their production and the Our present results and the knowledge that dogs adipose tissue by mobilizing more FFA to supply receiving Triton for a prolonged period of time energy to the parenchymal cells unable to utilize ultimately die, showing diffuse lipidosis and de- the other class of lipids. Lipoprotein proteins, pletion of fat stores (5), have led us to formulate not affected by Triton, maintain a normal metabo- a mechanism for the Triton disease in dogs as lism. Glucose, not apparently affected in its me- summarized in Figure 6. According to current tabolism by Triton administration (5), may pro- views (32), triglycerides bound to low-density vide the necessary energy source for fatty acid ,8-lipoproteins are the main form of transport of oxidation and lipogenesis. fatty acids moving from the liver to fat depots and other peripheral tissues, while FFA, bound SUM MARY mostly to albumin, represent the main form of transport of fatty acids moving in the opposite di- 1. Dogs fed a regular diet were given 250 mg rection. When Triton is administered to dogs of Triton (a non-ionic surface-active agent) and appropriate plasma levels are reached, the intravenously every fourth day. When sustained detergent, by combining preferentially with the hyperlipemia developed within a period of 3 to lipoprotein lipids (glycerides, cholesterol, and 4 weeks, the animals were injected intravenously phospholipids), modifies their surface property, with one of the following materials: lipoproteins transforming them into such foreign bodies as labeled with either cholesterol-4-C14 or P32-phos- will be removed by the reticuloendothelial cells. pholipids, C14-labeled chylomicron triglycerides, The establishment of a reticuloendothelial chan- I13'1-triolein, albumin-palmitate -l-C'4, I131-Triton, neling in the removal of lipids from circulation re- or lipoprotein labeled in the protein moiety with sults in lack of their uptake by the parenchymal I131. Normal dogs served as controls. 2. In cells of liver and adipose tissue. The liver then Triton-treated dogs, the rate of removal from circulation of the labeled triglycerides was 8 Plasma turnover rate = FFA (in ,uEq/ml) X lITt, markedly delayed. Such evidence was not ob- where Tt = half-time X 1.44. tained for labeled cholesterol and phospholipids, LIPID TRANSPORT IN TRITON-TREATED DOGS 503 leading to the belief that an increase of their he- 3. Hirsch, R. L., and Kellner, A. The pathogenesis of patic production was likely responsible for the hyperlipemia induced by means of surface-active hypercholesterolemia and hyperphospholipidemia agents. I. Increased total body cholesterol in mice given Triton WR 1339 parenterally. J. exp. Med. of dogs given Triton. 1956, 104, 1. 3. After administration of C14-palmitate, la- 4. Friedman, M., and Byers, S. 0. The mechanism re- beled plasma free fatty acids (FFA) exhibited an sponsible for the hypercholesterolemia induced by abnormal partition, being partly bound to albumin Triton WR-1339. J. exp. Med. 1953, 97, 117. but mostly associated with the class 5. Scanu, A., Oriente, P., Szajewski, J. M., McCor- low-density mack, L. J., and Page, I. H. Triton hyperlipemia of lipoproteins. From both compartments the in dogs. II. Atherosclerosis, diffuse lipidosis, and rate of removal from plasma of FFA was ap- depletion of fat stores produced by prolonged ad- proximately 2 minutes. It was estimated that ministration of the non-ionic surface-active agent. Triton-treated animals had a plasma turnover J. 'exp. Med. 1961, 114, 279. rate of FFA two to three times higher than had 6. Scanu, A., and Oriente, P. Triton hyperlipemia in dogs. I. In vitro effects of the detergent on se- normal animals. rum lipoproteins and chylomicrons. J. exp. Med. 4. Triton-treated dogs had normal levels of 1961, 113, 735. plasma lipoprotein proteins, which were removed 7. Scanu, A., and Hughes, W. L. Recombining capacity from circulation at normal rates. These proteins toward lipids of the protein moiety of human se- were associated with lipids floating at low and very rum al-lipoprotein. J. biol. Chem. 1960, 235, 2876. 8. McFarlane, A. S. Efficient trace-labelling of pro- low densities. teins with iodine. Nature (Lond.) 1958, 182, 53. 5. I131-Triton, injected into Triton-treated dogs, 9. Avigan, J. A method for incorporating cholesterol was removed from circulation at a slightly higher and other lipides into serum lipoproteins in vitro. rate than in normal animals. In normal dogs the J. biol. Chem. 1959, 234, 787. plasma radioactivity was contained in the high- 10. Havel, R. J., and Fredrickson, D. S. The metabo- lism of chylomicra. I. The removal of palmitic density (D 1.063-1.21) class. In Triton-treated acid-1-C1' labeled chylomicra from dog plasma. dogs, where this lipoprotein class is lacking, most J. clin. Invest. 1956, 35, 1025. of the radioactivity was in the low-density lipo- 11. Albrink, M. J., Glenn, W. W. L., Peters, J. 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